Introduction

Magnetic nanoparticles (MNPs) have attracted considerable attractions in different fields such as drug delivery [1], adsorption [2], catalyst [3, 4], MRI [5], antibacterial [6], and sensor [7]. Due to the unique inherent characteristics of magnetic nanoparticles (magnetic properties), it provides the possibility of recovering and reusing them in chemical reactions [8]. Also, the coating or modification of MNPs by organic, inorganic, and polymers such as polyethylene glycol (PEG) changes their morphology and improves their properties and selectivity [9]. PEGs (Macrogols) have been utilized as anti-freeze, lubricants, medical devices, food additives, and delivery of proteins and drugs. PEGs are not only used directly in the preparation of nanoparticles, but they can also be chemically linked or physically adsorbed onto nanoparticles [10]. There are a number of reports for the use of modified MNPs as adsorbents in removing the adsorption of water pollutants and as catalysts in the synthesis of organic compounds [3, 11, 12].

Water plays an essential role in the life of living organisms. With the advancement of science and technology, it has been contaminated by various pollutants such as dyes, heavy metals, bacteria, and organic compounds [13]. Due to the lack of clean water, the water purification process is very important. Heavy metals including copper (II) and iron (III)) are toxic and non-biodegradable. They can accumulate in human organs and other dwelling organisms and cause problems [14]. Despite the essential role of some metal ions such as copper and iron in the metabolic process of living organisms, the high concentrations of Cu (II) and Fe (III) in organisms cause many problems such as Alzheimer’s illness, Wilson disease, oxidative trauma, neurodegenerative syndromes, nervous disorders, anemia, cancers (breast, colorectal, liver, etc.), and diabetes [13, 15]. Therefore, the world health organization (WHO) stipulated the tolerable level for Cu (II) and Fe (III) ions about 2 mgL−1 and 0.2 mgL−1, respectively [16].

There are various methods to remove heavy metal ions in water such as ion exchange [17], electrodialysis [18], and membrane filtration [19]. However, these methods are expensive and have inadequate efficiency, the problem of membrane fouling, complicated operation process, and limitations in selectivity. Therefore, the use of an easy method with high efficiency and inexpensive is necessary. MNPs were utilized to improve the adsorption process and treatment of water.

Recently, significant progress has been made in the adsorption of heavy metals by magnetic nanoparticles (MNPs), such as the use of a composite of magnetite nanoparticles with a copolymer/silica coating for the removal of copper (II) [20,21,22,23].

In addition, MNPs have been used as a catalyst in the synthesis of heterocyclic compounds because of their easy separation by an external magnetic field and reusability several times [24,25,26,27]. The heterocyclic compounds of hexahydroquinolines and benzopyrans have attracted much attention due to their biological activities [28,29,30,31,32,33,34]. Although various methods have been reported for the synthesis of these compounds, some reports have disadvantages such as long reaction time, use of toxic solvents, or complete purification. Therefore, using catalysts with two or more metal cores to create an easy and inexpensive method for the synthesis of these compounds is a big challenge.

According to this report, we intend to study the effect of MnCoFe2O4@PEG-4000 MNPs as a nano-adsorbent for the removal of copper (II) and (III) metal ions in aqueous solutions and as a catalyst for the synthesis of hexahydroquinolines and benzopyrans.

Experimental

Material and methods

The materials were prepared by Merck Company and used without purification. The compound 5,5-dimethyl-3-(phenylamino)cyclohex-2-en-1-one (3) was synthesized according to the reported method [35]. The melting points of compounds were measured by Electro-Thermal 9100 apparatus. The progress of reactions was followed by thin layer chromatography (TLC) using aluminum plates, coated with silica gel with fluorescent indicator F254. FT-IR spectra were recorded in KBr pellet using Alpha Bruker spectrophotometer in the range of 400–4000 cm−1. The 1H- and 13C-NMR spectra were recorded on a Brucker Avence spectrometer at 300 and 75 MHz, respectively, using DMSO-d6 as a solvent and tetramethylsilane as an internal standard. The X-ray diffraction (XRD) was carried out by Philips X-pert Cu-Kα radiation (λ = 0.15406 nm) in the range of Bragg angle 10–80°. The field emission-scanning electron microscope (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were recorded by the TESCAN MIRA3 system. The magnetic properties of the MCF and MCF@PEG-4000 MNPs were investigated by the vibration sample magnetometer (VSM) with the model of 7300 VSM, Lake Shore Cryotronic, Inc., Westerville, OH, USA. Also, an atomic absorption spectrometer (AAS) with the model of AA-6800 Shimadzu was used to measure the amount of metal ion in an aqueous solution.

Synthesis of MnCoFe2O4 (MCF) MNPs

MnCoFe2O4 MNPs were prepared by the co-preparation method based on our previous report [36]. A mixture of MnCl2. 4H2O (2.5 mmol, 0.49 g), CoCl2. 6H2O (2.5 mmol, 0.59 g), FeCl3.6H2O (10 mmol, 2.7 g), and deionized water (100 mL) in the round bottom flask (250 mL) was heated at 95 °C for 1 h. Ammonium hydroxide (20%) was then added to the solution to adjust the pH to 12 and heated for another 1 h. The obtained black precipitate was separated by a magnetic field, washed several times with warm deionized water (200 mL) and ethanol (10 mL), and dried in the oven at 70 °C.

Synthesis of MnCoFe2O4@PEG-400 and MnCoFe2O4@PEG-4000 (MCF@PEG-400 and MCF@PEG-4000) MNPs

MnCoFe2O4 MNPs (1 g) and 100 mL of deionized water were sonicated for 20 min by ultrasound waves. Then, PEG-400 or −4000 (3 g) was added, and the mixture was stirred at room temperature for 24 h. The precipitate was isolated by a magnet and washed by deionized water to remove excess amount of PEG-400 or 4000 and dried in oven at 50 °C [37].

Synthesis of hexahydroquinolines (5a–h) and benzopyrans (6a–h)

A mixture of aryl aldehyde (1) (1 mmol), malononitrile (2) (1 mmol), 5,5-dimethyl-3-(phenylamino)cyclohex-2-en-1-one (3) (1 mmol) or dimedone (4) (1 mmol), and 0.01 g of MnCoFe2O4@PEG-4000 was refluxed in ethanol: water (6 mL, 1:1) as a solvent. After completion of the reaction (TLC), the solvent was evaporated, the mixture was diluted by ethanol (10 mL), and the catalyst was separated by an external magnetic field. The catalyst was well washed by ethanol to reuse in reaction. The product (5a–h or 6a–h) was filtered and dried in oven at 70 °C.

Adsorption and desorption studies of MnCoFe2O4@PEG-4000 MNPs

The adsorptive removal of Fe (III) and Cu (II) ions from aqueous solutions by MnCoFe2O4@PEG-4000 MNPs as a nano-adsorbent was investigated to optimize the adsorption conditions. All adsorption factors were studied by changing one factor, and other factors (pH range of 3–9), adsorbent dosage (5–20 mg), and metal concentration (25–200 ppm) were kept constant. After absorbing Fe (III) and Cu (II) ions from aqueous solutions, MnCoFe2O4@PEG-4000 MNPs were separated from the solution by an external magnetic fields, and the concentration of Fe (III) and Cu (II) ions remaining in the solution was determined by atomic absorption spectroscopy (AAS). The efficiency (%) and adsorption capacity (mg/g) were calculated by Eqs. 1 and 2, respectively. Where C0 and Ce are the initial and equilibrium concentration metal ions, respectively. In addition, V and m are the solution volume (in liters) and the adsorbent dosage (in grams), respectively.

Also, a regeneration study was carried out for the adsorptive removal of Cu (II) and Fe (III) in the presence of MnCoFe2O4@PEG-4000 as a nano-adsorbent. To study the cycle of adsorption experiments, the separated nanosorbent was washed several times with deionized water after the adsorption process. Then, the washed nano-adsorbent was treated with 3 mL of NaOH (0.1 M) for 60 min. At last, the regenerated absorbent was reused during three experiments for the removal of Cu (II) and Fe (III). The efficiency (RE%) was calculated by Eq. 3. In this equation, qre and qor are the adsorption capacities of the regenerated and original adsorbent, respectively [13].

$$R\%=\frac{C_0-{C}_e}{C_0}\times 100$$
(1)
$${q}_{eq}=\frac{C_0-{C}_e}{m}\times V$$
(2)
$$RE=\frac{q_{re}}{q_{or}}\times 100$$
(3)

Kinetic studies

The kinetic behavior of the adsorption process for metal ions was investigated by pseudo-first-order (Eq. 4) and pseudo-second-order models (Eq. 5) [13]. Where qe is the adsorbed amounts of metal ions of Cu (II) and Fe (III) at equilibrium, and the qt is the adsorbed amounts of metal ions of Cu (II) and Fe (III) at the time of t in the presence of MnCoFe2O4@PEG-4000 MNPs. Also, K1 (min−1) and K2 (g mg−1 min−1) are the pseudo-first-order constant and the pseudo-second-order constant, respectively.

$$\ln \left({q}_e-{q}_t\right)=\ln {q}_e-{K}_1t$$
(4)
$$\frac{t}{q_t}=\frac{1}{K_2{q}_e^2}+\frac{t}{q_e}$$
(5)

Adsorption isotherms models

In this study, two models of Langmuir (Eq. 6) and Freundlich (Eq. 7) were studied to describe the relation of extent of adsorptive removal of metal ions with their concentrations in solution at constant temperature [38]. Where, qe is the adsorption capacity at the equilibrium and qmax and K is saturated metal ion adsorbed amount and Langmuir constants. In addition, Ce is the equilibrium concentration of free metal ions. Kf is the Freundlich constant (L/g), and n is a constant, which is less than one (< 1) [23].

$$\frac{C_e}{q_e}=\frac{C_e}{q_{max}}+\frac{1}{bq_{max}}$$
(6)
$$Ln\ {q}_e= Ln{K}_f+ nLn\ {C}_e$$
(7)

Results and discussion

Catalytic study of MCF@PEG-4000 MNPs in the synthesis of hexahydroquinolines (5a–h) and benzopyrans (6a–h)

The catalytic activity of MCF@PEG 4000 MNPs was studied for the synthesis of hexahydroquinoline (5) and benzopyran (6) derivatives. Initially, treatment of 4-chlorobenzaldehyde, malononitrile, and 5,5-dimethyl-3-(phenylamino)cyclohex-2-en-1-one was selected as a model reaction for the synthesis of hexahydroquinolines (5). In this reaction, three parameters including solvent, amount of catalyst, and temperature were investigated to find the optimal conditions. The results are presented in Table 1. As data show, the best results for model reaction were obtained using 10 mg of MCF@PEG-4000 MNPs as a catalyst and using EtOH: H2O(1:1) as a solvent at 80 °C (entry 8, and Table 1). By increasing the amount of MnCoFe2O4@PEG-4000 catalyst from 5 mg to 10 mg, the yield is improved due to more available active sites of the catalyst. However, increasing the amount of catalyst above 10 mg leads to a decrease in the yield of the product, which may be due to the accumulation and a decrease in the surface of particles. Also, an increase in the temperature of reaction causes an increase in collisions between layers in the right direction, which in turn leads to an increase in yield of product and a decrease in reaction time. The optimum conditions for the synthesis of benzopyrans (6) were also investigated, and almost similar optimal conditions were obtained.

Table 1 The study of the optimal conditions for the model reaction in the presence of MCF@PEG-4000 MNPs as catalyst
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Also, the catalytic activity of MCF MNPs and MCF@PEG-4000 MNPs was compared to investigate the role of the PEG moiety (entries 8, 11, and 12). The results show that MCF@PEG-4000 MNPs have more catalytic activity than MCF MNPs. The presence of PEG-4000 as a coating on MCF MNPs improves the yield and reaction time due to the reduction of particle aggregation and the increase of available active sites. Moreover, the synthesis of hexahydroquinoline and benzopyran derivatives was performed in the presence of MCF@PEG-4000 as a catalyst under optimal conditions (Scheme 1), and the findings are presented in Table S2. In addition, the catalytic activity of MCF@PEG-4000 was compared with other reported catalysts in the literature (Table S3). The results confirmed that MCF@PEG-4000 has a perfect catalytic activity in the synthesis of hexahydroquinoline and benzopyran derivatives.

Scheme 1
scheme 1

Synthesis of hexahydroquinolines and benzopyrans in the presence of MCF@PEG-4000

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Reusability and recyclability of MCF@PEG-4000 for the synthesis of hexahydroquinolines (5b) and benzopyrans (6b)

The reusability and recyclability of MCF@PEG-4000 were investigated for the synthesis of hexahydroquinolines (5b) and benzopyrans (6b) during five runs under optimized conditions. After completion of the reaction, the solvent was evaporated, the hot ethanol (10 mL) was added to the mixture, and the catalyst was isolated by an external magnetic field. The reused catalyst was washed several time with hot ethanol (20 mL) and was dried in the oven at 70 °C. The reused catalyst was then used for five runs. The results are mentioned in Fig. 1a. As can see, the catalyst showed suitable catalytic activity during five runs with a little bit of decrease in efficiency. Also, the structure of reused and fresh catalyst were compared by their FT-IR spectra (Fig. 1b) and XRD patterns (Fig. 1c). Analyses do not show significant changes. The finding demonstrates that MCF@PEG-4000 has the appropriate reusability and recyclability during five times of use. Figure 1d shows the separation of the catalyst with the magnetic field after the completion of the reaction.

Fig. 1
figure 1

Reusability and recyclability of MCF@PEG-4000 MNPs in five runs (a), FT-IR spectra of the fresh and reused catalyst (b), XRD patterns of fresh and reused catalyst (c), and separation reused catalyst with the magnetic field after five runs (d)

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Suggested mechanism for the synthesis of hexahydroquinoline and benzopyran derivatives in the presence of MCF@PEG-4000 MNPs

The suggested mechanism for the synthesis of hexahydroquinoline and benzopyran derivatives in the presence of MCF@PEG-4000 MNPs is presented in Scheme 2. The catalyst activates the carbonyl groups of aldehyde (1) for condensation reaction with the enol form of malononitrile (2) to produce intermediated (A). Then, intermediated A and 5,5-dimethyl-3-(phenylamino)cyclohex-2-en-1-one (3) or dimedon (4) undergo a Michael reaction to produce intermediates B or C. Subsequently, a nucleophilic addition and tautomerization produce hexahydroquinoline (5) and benzopyran (6) derivatives [39].

Scheme 2
scheme 2

The suggested mechanism for synthesis of hexahydroquinoline and benzopyran derivatives in the presence of MnCoFe2O4@PEG-4000 MNPs

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Adsorption studies

Effect of the initial pH

The pH of the solution is a major factor in controlling the metal ions’ adsorption onto the surface adsorbent [40]. This parameter plays a key role in describing the adsorption mechanism by changing the surface charge of the adsorbent. The chemical interaction (columbic attraction) and electrostatic force (repulsion between reactive sites of MCF@PEG and adsorbing ions) are two main forces for the adsorption processes [41]. As shown in Fig. 2a, the pH values affect the adsorptive removal efficiency of Cu (II) and Fe (III) ions. The adsorptive removal process was performed at pH 3, 5, 6, 7, and 9 (room temperature) with an amount of 0.01 g of MCF@PEG-4000 for 30 min. Then, adsorption capacity (q) was calculated for both ions at different pHs. Increasing pH increases the adsorption capacity and the efficiency of ions. At acidic pH, the active sites of MCF@PEG are protonated, the repulsion between MCF@PEG and ions occurs, and the adsorption of metal ions is decreased [40]. At alkaline pH, the adsorption capacity shows little change due to the competition between OH− ions and the adsorbent to remove the ions, which is consistent with the adsorption mechanism of the metal-OH complex [42]. In addition, Fe (III) ions show more sensitivity to pH change than Cu (II) ions. As a result, an initial pH of 7 was selected for the adsorption process of Cu (II). The results confirm that the adsorption capacity for Cu (II) is more than that of Fe (III), and the maximum adsorption capacity (qmax) for both ions is obtained at pH = 7.

Fig. 2
figure 2

The effect of pH, dosage, concentration, and contact time on adsorptive removal of Fe (III) and Cu (II)

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Effect of the adsorbent dosage

The effect of adsorbent dosage on the adsorption of Cu (II) and Fe (III) ions at pH = 7 was investigated. The experiment was performed in the presence of different amounts of MCF@PEG-4000 MNPs (5, 10, 15, and 20 mg) (Fig. 2b). The findings showed that increasing the amount of adsorbent from 5 to 10 mg increases the adsorption capacity (q) of both ions (Cu (II) and Fe (III)). This increase could be related to the increase of active adsorption sites available for the adsorptive removal process [40]. Nevertheless, with the adsorbent dosage up to 20 mg, a decrease on adsorption capacity is observed, which can be due to the accumulation of particles and the decrease of the adsorbent surface [43]. Hence, 10 mg of the nano-adsorbent was selected as the optimal amount of adsorbent for the adsorption process.

Effect of initial concentration

The results showed that there is a direct ratio between the removal efficiency and the initial concentration of metal ions (the removal efficiency increases as the initial concentration increases, Fig. 2c). R% for Cu (II) at concentrations of 25, 50, 100, and 200 ppm were calculated as 99.91, 99.86, 99.95, and 99.93%, while this parameter was found to be 99.05, 99.71, 99.9, and 99.90% for Fe (III), respectively. The increase of adsorption capacity at high metal concentrations can be due to the higher adsorption rate and the use of all available active sites of the adsorbent [43]. Also, the data confirm that with an increase in initial concentration, the removal efficiency at a fixed adsorbent dosage for Fe (III) and Cu (II) ions increases and is almost the same for both. However, the data show a decrease in the removal efficiency of copper (II) from 100 to 200 ppm, which can be related to the saturation of the active sites present on the absorbent at a concentration of 200 ppm Cu (II). The results are consistent with the results of Samarjian’s report [44]. Also, the results show that the effect of the initial concentration on the removal percentage of heavy metal ions by the magnetic nanosorbent is highly dependent on the initial concentration of metal ions [43, 45].

Effect of the contact time

The versus effect of contact time (5–200 min) on Fe (III) and Cu (II) ions’ adsorption in the presence of MCF@PEG-4000 is presented in Fig. 2d. The finding describes adsorptive removal efficiency increase for both metal ions by the adsorbent with an increase the contact time. The adsorptive removal process shows the high rapid adsorption and an increase of adsorptive removal efficiency from 5 to 30 min that confirm with the increase of contact time to 30 min, the interaction between the adsorbent and ions has been well done. Also, it observes a decrease of adsorptive removal efficiency with an increase of contact time from 30 to 200 min. Maximum removal adsorption for both ions was observed within 30 min with the adsorptive removal efficiency of 99.93% and 99.94% for Cu (II) and Fe (III), respectively, which is dramatically short time in compare to previous works [46]. According to Fig. 2d, the removal efficiency of Fe (III) ions is about at 30–120 times greater than that of Cu (II) ions. This may be attributed to the high affinity of Fe (III) ions for MCF@PEG-4000 compared to Cu (II) ions [47].

Effect of PEG-coating

The effect of PEG-coating on the adsorptive removal process was investigated under optimal conditions (pH = 7, 30 min, and 0.01 g of adsorbent). The R% and qe were calculated for MCF, MCF@PEG-400, and MCF@PEG-4000 MNPs and are mentioned in Table 2. The obtained data show that the modification of MCF MNPs with PEG improves the adsorption process about only 0.9%, which is not very impressive. However, this improvement of the adsorptive removal process can be related to the decrease of MCF accumulation due to surface modification with PEG and increasing of active sites [48]. In fact, The adsorption capacity increases with the degree of functionalization [45].

Table 2 The effect of PEG-coating on adsorptive removal process under optimal conditions
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Kinetic studies

Adsorption isotherms

The different adsorption isotherm models have been used to describe adsorption processes and the probable mechanism for the adsorptive removal process. The obtained data were fitted to the two-adsorption isotherm models (Langmuir and Frendlich models, Figs. 3a and b), and the results are presented in Table 3. The obtained data were fitted to the two-adsorption isotherm models (Langmuir and Frendlich models, Figs. 3a and b), and the results are presented in Table 4. Regression coefficient values of the Langmuir isotherm model were numerated for both metal ions, R2Cu = 0.81 and R2Fe = 0.84, while regression coefficient values of the Frendlich model were obtained for both ions R2Cu = 0.97 and R2Fe = 0.99. Calculation confirmed that the Frendlich model was more adequate than the Langmuir model for Cu (II) and Fe (III). In addition, the RL, Kf, and qmax values were calculated for Cu (II) ions at 18.18 (L/mg), 23.79 (L/g), and 555.5 (mg/g), respectively, while these values were calculated for Fe (III) ions at 0.79 (L/mg), 11.7 (L/g), and 666.6 (mg/g), respectively, which indicated the Fe (III) and Cu (II) adsorption onto MCF@PEG-4000 MNPs is desirable under the Frendlich isotherm model. The Frendlich isotherm model describes the multilayer adsorption of Fe (III) and Cu (II) ions on the surface of the nano-adsorbent [49].

Fig. 3
figure 3

The Langmuir isotherm model (a) and the Frendlich isotherm model (b)

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Table 3 The obtained data from the Langmuir isotherm and Frendlich isotherm models
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Table 4 The obtained data from the pseudo-first-order and the pseudo-second-order models in adsorptive removal of Cu (II) and Fe (II)
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Kinetic of adsorption

The data of the pseudo-first-order and the pseudo-second-order models were presented in Table 4 and Fig. 4a and b. As the results show, the correlation coefficients (R2) of the pseudo-second-order model for both metal ions are close to one, which confirms that the adsorptive removal process follows the pseudo-second-order model. This model can predict the interaction between adsorbed metals (Cu (II) and Fe (III)) and adsorbent (MCF@PEG-4000). In addition, the calculated equilibrium adsorption of Cu (II) and Fe (III) ions was in agreement with the experimental equilibrium adsorption for both metal ions (Table 4). Findings indicate that electron transfer and the chemical adsorption are the rate-limiting step in the adsorption process [50, 51]. In addition, the adsorption rate (K2) for Cu (II) and Fe (III) was calculated to be about 2.27 and 0.96 g/mg min−1, respectively. The obtained results show that the adsorption rate of Cu (II) is higher than that of Fe (III). Overall, MCF@PEG-4000 MNPs can rapidly remove Cu (II) and Fe (III) from aqueous solution. Comparison of q values for several adsorbents (entries 1–8) in the Table 5 shows that MCF@PEG-400 MNP is a suitable adsorbent for the removal of iron and copper Cu (II) and Fe (III) in aqueous solutions.

Fig. 4
figure 4

The pseudo-first-order (a) and the pseudo-second-order models (b) for adsorptive removal of Cu (II) and Fe (III) ions in aqueous solution

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Table 5 The comparison of qmax for removal of Cu (II) and Fe (III) in this work with other reports
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Regeneration study for MCF@PEG-4000 MNPs adsorbent

A regeneration study of MCF@PEG-4000 MNPs for adsorptive removal of Cu (II) and Fe (III) ions in aqueous solution was investigated (Fig. 5). After separation of MCF@PEG-4000, the adsorbent was washed by NaOH (0.1 M) and water to regenerate adsorption sites on the surface of the adsorbent. The regenerated adsorbent was reused during three experiments for the adsorptive removal of Cu (II) and Fe (III). The results are mentioned in below column chart. The data confirmed that MCF@PEG-4000 could be used for five times without a dramatic change in the removal efficiency (R%).

Fig. 5
figure 5

The obtained results from a regeneration study of the MCF@PEG-4000 MNPs adsorbent

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In summary, the active sites of MNPs are increased due to the presence of Mn and Co ions to improve the adsorption process and catalytic activity [58]. The obtained results from the study of adsorption kinetics and isotherms indicate the fact that the adsorptive removal of ions is in accordance with the pseudo-second-order models and the Freundlich isotherm. The findings describe an interaction between heavy metals and the OH groups of PEG coated on the absorbent surface. The obtained results from the effect of pH confirm that the ability of these functional groups in the adsorptive removal of metal ions depends on the pH of the solution [59, 60]. In addition, the use of MCF@PEG-4000 MNPs as the catalyst showed excellent catalytic activity for the synthesis of hexahydroquinolines and benzopyrans.

Conclusion

In this work, MCF@PEG-4000 magnetic nanoparticles were prepared by a clean and simple method. The use of PEG as a green and environmentally friendly coating improves the use of these nanoparticles as a catalyst in the synthesis of organic compounds such as hexahydroquinolines and benzopyrans and as an adsorbent for the adsorption of heavy metals such as iron and copper in aqueous solution. High efficiency, short reaction time, and easy separation of the catalyst are among the advantages of MCF@PEG-4000 nanoparticles as a catalyst in the synthesis of hexahydroquinolines and benzopyrans. Furthermore, the adsorption activity of MCF@PEG-4000 MNPs as an adsorbent to remove Cu (II) and Fe (III) metal ions in aqueous solution under optimal conditions for Cu (II) and Fe (III) was found to be about 149.90 and 298.82 mg/g, respectively.